Chemical analysis on river/dam water and river gravels have been done in order to clarify the cause of black-staining on river gravels. The black-stained gravels are deposited scattered only in downstream of the dam. Based on chemical analysis, black outer part of the gravels has much higher Mn content than core, indicating that precipitation of Mn-oxide causes the blackening. Mn concentration of the river water is significantly higher in downstream than in upstream of the dam, and that of the dam water noticeably increases in summer at deeper than 10 m. These field observation and chemical analysis data suggest that Mn-leaching in summer at the bottom of the dam causes the formation of the black-stained gravels at the downstream.

View full abstract

Before the soil contamination is investigated on the ground, there are soft information about soil contamination in many case. Soft information will suggest the possibility of soil contamination but it is vague such as ″This area may be high concentration but there is no surveyed data.″ So there are few methods in order to search optimal arrangement of sampling location using soft information. In this study, optimal arrangement of sampling location was decided by geostatistics method using informative prior distribution in order to apply soft information. The result showed that using soft information is more suitable than using non information in order to decide optimal arrangement of sampling location. Geostatistics method can also apply the previous survey of the general condition of soil contamination. One stage sampling plan is that all sampling location has decided in one time. Multiple stage sampling plan is that some sampling location has been decided and gives information to next arrangement of sampling location. When the number of total sampling points is equal, multiple stage sampling plan is more suitable than one stage sampling plan.

View full abstract

Applicability of densification method by means of controlled blasting is examined by three field tests, and design formulae are proposed. Sand, silt and fill grounds are examined. Blasting is designed to install in the borehole which are arranged with several meters distance from each other, and fired with a little time lags. Water boiled out from the ground and the ground surface subsided after blasting. Since the SPT-N values increases according to the settlement of the ground, it can be used as remedial measures against soil liquefaction. The ground settled significantly just after the blasting, and terminates for several days. Duration of settlement increases up to several weeks as fines contents increases. Improvement of the ground strongly depends on the amount of blasting per unit volume. It is also affected by delay time and distance between boreholes. Although increase of SPT-N value becomes smaller as fines contents increase, the method is applicable to the ground with fines contents larger than 40 %. The vibration of the ground can be predicted from the data by single blasting or preliminary test, and vibration in the vicinity of the site can be reduced by controlling the blasting conditions.

View full abstract

In this paper, a series of loading tests on sand ground were conducted under both gravitational field and centrifuge force field. A newly developed image analysis method, CCIP method (Cross Correlation and IsoParameteric method) was used to observe the deformation behaviour of sand ground. Main conclusions are drawn as follow: According to the load-settlement relationship curves, typical general shearing failure could have occurred inside the ground. However, it was proved by the observation of deformation behaviours in the tests that a pattern of progressive deformation and progressive failure happened. Before the peak of load, the main type of deformation in sand ground is compressive deformation. Passive zone, including intermediate zone, did not appear clearly in this stage. The main difference of deformation behaviour between gravitational tests and centrifugal tests is the compressive deformation. The shear zones of these two kinds of test showed almost same distributions.

View full abstract

The changes in climate all over the world have brought various natural disasters such as flood, drought and so on. In Japan various types of slope failures due to rainfall often occur in the rainy season. Therefore Kitamura et al. have proposed a prevention system of slope failures due to rainfall. In this paper, the soil tank tests are carried out in order to analyze the mechanism of slope failure due to rainfall. The pore-water pressure in the soil is measured by the tensiometers and pore-water pressure sensors. The experimental results are compared each other, and the seepage and failure behaviors of Shirasu slope during rainfall are analyzed.

View full abstract

In this paper, a variability of undrained strength of alluvial clay subjected to aging effect which was investigated by cone penetration test (CPT) and unconfined compression test (UCT) is discussed. In general, the soil parameters taken from CPT have a small variability compare with unconfined compression strength (q_u. value). To study the variability of undrained strength, CPT and UCT were carried out at Osaka Bay where uniformly alluvial clay is deposited. The main conclusion as follows ;
1) The coefficient of variation of undrained strength taken from CPT is below the half compare with q_u. value.
2) The difference of the variability was caused the aging structure of clay.
3) The variability of undrained strength have a tendency to decrease with consolidation of clay and the coefficient of variation show a constant value.

View full abstract

This paper describes uplift behavior of full-scaled ground reinforcing type foundation in sandy ground. This new type of foundation is developed with the idea of reinforced earth method to meet the increase of uplift bearing capacity of transmission tower foundation. Uplift loading test of full-scaled foundation, with the diameter of 2.5m, the depth of 8m and 20 steel bars inserted in the surrounding ground, was carried out in sandy ground in order to investigate the reinforcement mechanism of the steel bars. From the test results, especially the detailed measurements of the behaviors of the foundation, the steel bars and the surrounding ground, it is recognized that the reinforcement effect for the increase of uplift bearing capacity is quantitatively evaluated as the sum of two kinds of effects. One is the reinforced soil effect, which restrains the dilatancy of surrounding ground, and another is structural effect of the steel bar itself.

View full abstract

The amount of deformation in the slope collapse represents the index of quantitative evaluation, and the Newmark method is one of the recognized evaluation methods applied for the embankment. There is no seismic response acceleration of the embankment but the ground acceleration that shows seismic force on the slide clod with the usual Newmark method. However, the embankment itself seismic response properties weren′t taken into consideration by this perspective, so the modified Newmark method, with the seismic response character added by modeling the embankment with the SDOF model was proposed. Therefore we must compute the natural frequency of embankments accuracy and easily in the seismic design. So, in this study, a simple calculation method of the natural frequency in consideration of the shape of embankments was derived by using Rayleigh′s method, the validity of the proposed formulation in comparison of the result of shaking table tests and theoretical calculation.
That was examined as the results, the natural frequency of embankments can be computed accuracy and easily from the proposed method. And, we indicated that the result of calculation of the seismic permanent displacement of embankments varies in the adopting method of computation of the natural period with the modified Newmark method very greatly.

View full abstract

The lack of accessibility of the rural access roads has been identified as one of the main causes of poverty of the rural people in Papua New Guinea. In this study, the new design for all-weather rural access road with ″do-nou″ (which is Japanese term for soilbag) is being developed. In the new design, the maintenance is conducted only by manual labour and available materials in Papua New Guinea, therefore the local farmers can participate in the process of the restoration of the road. In the villages in Papua New Guinea, real constructions based on the proposed method were conducted with the rural people. Through the constructions, the practicability was demonstrated. The method to maintain unpaved road with ″do-nou″ can contribute to keep the trafficability of the road whose traffic is below 10 vehicles per day. The motivation of the villagers to participate in the road maintenance constructions depends on the location of the village. If the cheap but necessary fee for the material of the do-nou method is supported, motivated villagers can maintain the unpaved road by themselves. In the collaboration with a Member of Parliament, the system to keep the trafficability sustainably could be in operation.

View full abstract

In the case where soft bottom mud with high water content over the liquid limit is fluidized by the pressure induced by waves, cracks are generated in the surface of the mud. The cracks develop under the action of tensile stress and shear stress caused by the rotation of principal stress in the periodic motion of waves. It is found that the dredged mud, which contains the smectite as clay mineral, fails developing definite deep cracks so that ductile mass of clay can be retained. The effect of the cracks on the acceleration of consolidation of the mud is reproduced and evaluated by a numerical analysis and experiment of self-weight consolidation with the placement of vertical drains. The mechanism of the acceleration of consolidation of the mud by wave action is elucidated through experimental and numerical studies.

View full abstract

Industrial waste disposal is an increasing problem in recent years. It is, therefore, becoming increasingly important for technology and engineering design to be utilized effectively for industrial waste disposal. Waste plasterboard is generated in vast quantities as a by product of demolition of buildings and houses. If waste plasterboard can be effectively utilized as a construction material, the problem of waste plasterboard disposal and shortage of natural resources for construction may be solved. It is also environmentally friendly, due to its neutral nature. This paper describes the unconfined compressive strength of cement-stabilized soils mixed with bassanite produced from waste plasterboard to promote waste plasterboard recycling. Bassanite is produced by heating gypsum obtained from waste plasterboard, under conditions of 130°C or more. The strengths of samples were determined by unconfined compression tests after 28 days curing immediately after molding. The effects of bassanite contents on stress-strain behavior of cement-stabilized soils are quantified. The unconfined compressive strength increases with increase in bassanite contents. This is due to concomitant decrease in the water content. These properties make bassanite produced from waste plasterboard useful as a construction material. The potential use of waste plasterboard can be refined with further research.

View full abstract

Utilization of waste plasterboard as geomaterial solves a solid waste disposal problem, and also provides needed construction material. Waste disposal problems of waste plasterboard are becoming acute in the urban environment, because it is here that most waste plasterboard generating sites are located, and where the supply of natural construction aggregate is becoming scarce. Bassanite is produced by heating gypsum obtained from waste plasterboard, under conditions of 130°C or more. It is also environmentally friendly, due to its neutral nature. This paper presents the compaction properties and unconfined compressive strength of bassanite produced from waste plasterboard. Effect of bassanite additions on unconfined compacted soils is also investigated. The samples were compacted, and strengths determined by unconfined compression tests after 28 days of curing immediately after compaction. The optimum water content of bassanite-sand mixtures increases and the maximum dry density decreases with increase in bassanite content. The unconfined compressive strength of compacted bassanite-sand mixtures decreases linearly with increasing water content, irrespective of bassanite content. In contrast, the unconfined compressive strength of compacted bassanite-clay mixtures drops off sharply on the wet side of optimum water content, whereas on the dry side it increases with increasing water content, irrespective of bassanite content.

View full abstract

Most of old fill-dams were accumulated with a muddy soil in reservoir. This muddy soil is generally very soft clayey soil accompanied with the changes of the water content and the grading. In order to make efficient use of such a muddy soil as embankment soil, we have developed a new type method to repair the damaged embankment by the cement-mixed muddy soil. The strength and strain behavior of the cement-mixed muddy soil is influenced considerably by the water content and the grading of muddy soil. We propose a strength control method considering the effect of the grading and the water content of muddy soil on the cement-mixed muddy soil, and proved the proposed method by the site investigation test under actual condition.

View full abstract